In prior beverage dispensing devices substantial quantities of beverages have been lost through spillage resulting from malfunctioning valves. Also customer dissatisfaction with automatic beverage dispensing devices especially automatic beer dispensers has resulted from their failure to pour consistently preselected quantities.
Beverage dispensing devices and beer dispensing devices in particular have in common a faucet or shank forming a passageway for connection to a beverage source through flexible tubing and a beverage outlet spout. A valve seat is provided within the faucet for seating a sealing member. A valve housing has a first end in open communication with the valve seat, and an opposing open end to which a valve actuator ball pivot is threadedly attached. A valve stem contained in the housing interconnects the sealing member to the valve actuator. One end of the valve stem is connected to the sealing member; the opposite end of the valve stem is provided with a pair of spaced pistons. The actuator lever has an end connected between the spaced pistons of the valve stem. Thus, the valve actuator engages the pistons to seat and unseat the sealing member. A problem with these devices is that in disassembling the valve for cleaning and reassembling the device the actuator can be overtightened thereby increasing the force required to operate the valve.
In known valve designs there is no seal to prevent the beverage from entering the piston/housing area. The beverage over a period of time evaporates and leaves a solid residue which builds up to retard operation of the valve actuator. If the residue is not removed the pistons will seize. Beer is particularly bad. The yeast and other solids in beer solidify with time. During solidification increasing force is required for the actuator to open and close the sealing member. Thus, periodically the actuator must be removed, the valve disassembled and the pistons and cylinder cleaned to prevent complete immobilization of the valve and the formation of harmful bacteria.
In automatic beverage dispensing systems such as automatic beer dispensers, the actuator is connected to a computer controlled solenoid. This additional structure adds to the difficulty in disassembling the faucet for cleaning. Further, with the need for increasing valve operating pressure, careful control of the temperature and pressure cannot prevent variations in the amount poured. To achieve commercial success for automatic beverage dispensing systems, various approaches to the cleaning problems have been made.
An approach for solving the cleaning problem has been to design the faucet to facilitate disassembly. This approach included the addition of quick release couplers for mounting the housing on the faucet and a slip joint connection between the electrically powered valve-operated part and the valve stem. These features allow unobstructed access to the valve stem when the dispenser is removed from the system. Those persons skilled in the art desiring more information about such a dispenser are referred to U.S. Pat. No. 4,111,243 issued Sept. 5, 1978 to Fetterman. While this approach provides easy access to the valve for cleaning, no structure is included to prevent solid buildup in the valve which causes the sticking problem.
Another approach to the problem was to design a faucet so as to reduce the force required to operate the valve. In this approach the valve housing is provided with a pair of spaced O-rings formed of a low friction material (polytetrafluoroethylene). These O-rings engage the spaced pistons of the valve stem on both sides of the actuator lever. Thus, the diameters of the spaced pistons can be reduced to increase the space between the pistons and cylinder, and to reduce the force necessary to manipulate the valve stem between the flow preventing and flow permitting positions. Those persons skilled in the art desiring more information about this structure are referred to U.S. Pat. No. 3,718,233 issued Feb. 27, 1973 to Nordhoff. A problem with this structure lies in the required positioning of the O-rings. The O-rings are positioned well within the cylinder area. Thus, although seepage is reduced between the O-rings, damaging build up of solids on the stem areas which extend into the valve housing beyond the O-rings can occur. This buildup of solids will ultimately result in the sticking of the valve.
For customer acceptance of automatic beverage dispensers, it is essential that the amount of beverage poured be accurate. Pressure and temperature are factors which contribute substantially to the pouring accuracy of automatic beverage dispenser systems. It is well known that liquid of any kind flowing in a line meets resistance to flow, or "drag". Drag in a line is a function of the size, material, and interior smoothness. Thus, drag results in a continuous drop in pressure throughout the total line length and is measured in pounds per square inch per inch. Changes in applied pressure at the beginning of a line of fixed length, size, and material results in a change in the rate of flow of liquid in the line; however, because of drag the flow of a liquid in the line is not linear. Thus, doubling the applied pressure will result in less than twice the rate of flow and correspondingly, reducing the applied pressure by one half of the previous setting will result in a reduction in flow of less than fifty percent. As the flow rate of fluid in a line is not linear and is dependent on the physical properties of the line it is difficult to measure a quantity based on pressure and temperature alone.
One means for accurately determining the quantity dispensed is to use pressure transducers to measure the flow rate of the liquid and calculate the time required to dispense a preselected quantity. Pressure sensors for flow meters, however, are very sensitive to pressure shock. Any sudden increase in pressure on one side of a differential pressure transducer will damage most pressure transducers. Sudden pressure increases exist as shock waves (water hammer) when a flowing liquid is abruptly stopped by the substantially instantaneous closing of the valve. Further, with existing flow meters the pressure difference transducers, such as those used in manometers, measure pressure differences indicated by difference in head measurements which are very small and required a substantial amount of amplification.